Lysine 2,3-aminomutase: is adenosylmethionine a poor man's adenosylcobalamin?

The interconversion of lysine and beta-lysine, which is catalyzed by lysine 2,3-aminomutase, is formally similar to the isomerization reactions catalyzed by adenosylcobalamin-dependent aminomutases. However, lysine 2,3-aminomutase is activated by S-adensoylmethionine and not by adenosylcobalamin. Lysine 2,3-aminomutase also contains [FeS] clusters, Co(II), and pyridoxal 5'-phosphate, all of which are required for maximum activity. Lysine 2,3-aminomutase acts through a mechanism akin to that of the adenosylcobalamin-dependent enzymes in which substrate radicals are intermediates. However, the 5'-deoxyadenosyl moiety of S-adenosylmethionine mediates hydrogen transfer in place of the 5'-deoxyadenosyl moiety of adenosylcobalamin. 5'-Deoxyadenosine is an intermediate in adenosylcobalamin-dependent reactions and in the reaction of lysine 2,3-aminomutase. The 5'-deoxyadenosyl radical, derived either from adenosylcobalamin or S-adenosylmethionine, appears to participate in these reactions. Similarly, the ribonucleotide reductase from Lactobacillus leichmanii is activated by adenosylcobalamin, whereas the ribonucleotide reductase from anaerobically grown Escherichia coli is activated by S-adenosylmethionine and an activating enzyme. The 5'-deoxyadenosyl radical seems to participate in the activation of both reductases. Therefore, both adenosylcobalamin and S-adenosylmethionine appear to serve as sources of 5'-deoxyadenosyl radicals in nature. S-Adenosylmethionine is not as chemically elegant a molecule as adenosylcobalamin, so it may be regarded as "a poor man's adenosylcobalamin."